Adjustable contact converter



Feb. 19, 1957 F. KOPPELMANN ADJUSTABLE CONTACT CONVERTER s sheets-het 1Flled March 25, 1953 Feb. 19, 1957 F. KOPPELMANN 2,782,359

ADJUSTABLE CONTACT CONVERTER Filed March 25, 1953 f 3 Sheets-Sheet 2 v l7 f F/g.2

CDNTRUL DEVICE if v '-77 5a y Z'm/enof:

Feb. 19, 1957 F. KOPPELMANN 2,782,359

ADJUSTABLE CONTACT CONVERTER Filed March 25, 1953 Sheets-Sheet 3 Figs,al 1

Inventor.'

FLORIS KoPPELmA/Y/ United States Patent 2,'7s2,ssa

ADJUSTABLE CoNrAcr convnnrnri Floris Koppelmann, Berlin-Siemensstadt,Germany, ns-

sgnor to Licentie Patent-Verwaltungs@ m. h. H., Hamburg, GermanyApplication March 25, 1953, Serial No. 344,6@

19 Claims. (Cl. S21-48) The present invention relates to mechanicalrectitiers or contact converters, particularly (though not exclusively)to converters of this type designed for large power outputs.

lt is known to provide contact converters with means for varying theoutput thereof by shifting the periods of contact closure with respectto the phase of the alternating input voltages, whereby (in analogy withthe output control through phase shaft in the case of electronicrectiflers) the amount of power delivered to a load can be adjusted atwill or else maintained substantially constant in the face of varyingoperating conditions. A drawback of these known arrangements resides inthe fact that displacement of the closure periods of the rectifiercontacts will cause the contacts to close at instants when a substantialvoltage is present across these contacts and/or to open while a largecurrent passes therethrough, thereby resulting in arcing and in theeventual destruction of the contact surfaces.

It is, accordingly, an object of the present invention to provide meansfor so controlling a converter of the character set forth as to enableadjustment of its output without incurring the danger' of undesirabledischarges at the contact surfaces. More specifically, it is an objectof this invention to provide means for shifting the phase of theintermittent current with respect to that of the alternating voltage incombination with mechanism for invariably closing the contacts of theconverter substantially upon the occurrence of a voltage nodethereacross and for invariably opening said contacts at a time ofsubstantially minimum current flow therethrough.

The above objects are realized, in accordance with the presentinvention, by the provision of saturable electromagnetic reactance meansfor periodically including a high impedance in series with themechanically actuated contacts, phase shifting means for varying therhythm of saturation of said reactance means with respect to thephase ofthe input voltage, and a timer mechanism coupled to said phase shiftingmeans and maintaining the cut-in of the contacts in ixed phaserelationship with the input voltage while displacing the cut-out of thecontacts in step with the dephasing of the saturation of said reactancemeans so that this cut-out will occur at a time when the reactance inseries with the contacts is large enough to reduce the flow of currenttherethrough substantially to zero. in the case of polyphase inputvoltages, more particularly, the cut-in of the contacts will becontrolled to coincide with the junction of successive phase voltages,i. e. to occur at a time when the instantaneous value of the descendingportion of one voltage phase equals the instantaneous value of theascending portion of the next phase.

The invention will be better understood from the following detaileddescription, reference being had to the accompanying drawing in which:

Fig. l is a set of graphs serving to explain the principles underlyingthe present invention;

ICS

Fig. 2 shows, partly diagrammatically, a contact converter according tothis invention;

Pig. 3 is a fragmentary view of a converter representing a modificationof that shown in Fig. 2; and

Fig. 4 is a diagrammatic View of the control device used in theembodiments of Figs. 2 and 3.

Graph (a), Fig. l, shows the phase voltages u, v, w of a three-phasenetwork 1, Fig. 2, connected to the input of a converter according tothis invention. An input transformer 2 comprises three primary phasewindings Su, 3v, 3W, delta-connected to the respective conductors ofnetwork 1, and three secondary phase windings 4u, 4v, 4W, Y-connected inseries with respective main windings 11, 12, 13 of saturable-corereactors S, 6, 7 whose cores are shown at 8, 9, 1@ bearing biasingwindings 14, 15, 16. The neutral point of the Y of the secondarytransformer windings is connected via a smoothing choke 27, having anarmature 23, to one terminal of a load 29; the other load terminal isconnected to a control device 76 and thence returned, in parallel overpairs of contacts 118-19, 2li- 21, 22-23, to the main reactor windings11, i2, 13.

The contacts of each of the aforesaid pairs are intermittently andperiodically interconnected by bridge pieces 24, 25, 26, respectively7mounted on rods 4Z, 43, 44. These rods are pivotally connected at 33,34, 35 to intermediate points of arms 30, 31, 32, respectively, each ofwhich has one extremity linked at 36, 37, 3S to a depending piston 39,all, 41 guided in a sleeve d5, d6, 47, respectively. A shaft 51, formingan extension of the rotor 53 of a motor 52 which may be energized fromthe mains 1 over connections not shown, bears three staggered cams d8,49, 50 of roughly crescent-shaped cross section, these cams cooperatingwith the pistons 39, dll, 41, respectively. The housing 54 of the motor52, held in suitable supports (not shown), is angularly displaceablewithin certain limits, as indicated by an arrow, for a purpose presentlyto be described.

The other extremity of each of the arms 3l), 31, 32, indicated at 72,73, 74, is fulcrurned on a rod 71. A bell crank lever composed of twoarms 58, 61, and pivoted at the junction 62 of said arms to a ixedbracket 60, bears the rod 71 at the free end 75 of its shorter arm 61and carries a roller or cam follower 57 on the free end of its longerarm 5S. The roller 57 rides on the curved surface of a cam member 55which is lixedly mounted on the housing 54 of motor 52 and is urged intocontact with the roller by a spring 56.

A variorneter or phase shifter 66 has a shaft 65 which carries a crankarm 64, the latter being linked at 69 to a lever 63 which at 59pivotally engages an intermediate portion of the long arm 53 of bellcrank lever 58, 61. The position of shaft 65, and, thereby, that of arms64, 63, 5S and 61, is controlled by way of suitable transmission means,indicated schematically at 77, from the device 76 which may be acurrent-sensitive governor of, for example, the oil pressure type. Theinput to the variometer 66 is constituted by three conductors 70connected to respective phase conductors of the network 1; the outputcircuit of the variometer comprises three similar conductors 67connected in a Y to biasing windings 14, 15, 16, respectively.

The operation of the system of Fig. 2 will be described with furtherreference to Fig. l, where graph (b) shows at iv and iw the currents dueto the phase voltages v and w, respectively. Let us assume that theconnector 25, associated with the phase v, makes (i. e. interconnects itcontacts 20 and 21) at a time to when the instantaneous values of phasevoltages u and v are equal, thus at an intersection of the correspondingcurves shown in graph (a). Since contacts 18, 19 of the preceding phaseare still closed at 24 when the connector 25 descends, contact 21 willbe substantially at potential u whereas contact 2t) will besubstantially at potential v, so that virtually no voltage differencewill exist across the two contacts to be bridged by the member 25; thusthe cut-in will take place without areing.

it will be noted that the circuit now closed by the connector 25 (and,analogously, each of the circuits adapted to be closed by connectors 24and 26) comprises two distinct reactances, namely the smoothinginductance 27 common to the three phase circuits and the inductance ofthe respective reactor, such as 6, individual to this one circuit. Thusthe buildup of the current iv through winding 12 will be determined bythe reactor impedance and, hence, by the degree of saturation of core 9by biasing winding 15, whereas the commo-n smoothing means of the loadcircuit, such as choke 27, will tend to maintain constant the totalcurrent drawn` by the load 29. lf the reactor 6 becomes saturated withthe proper polarity soon after the time to, the current iv may riserelatively rapidly to its maximum which it reaches at a time t1, thecurrent in (not illustrated) through contacts 1S, 19 decaying at thesame time to substantially zero whereupon the connector 24 is allowed tolift. At a time t2, when the instantaneous phase voltages v and w areequal, connector 26 closes without arcing and causes a current iw topass through contacts 22, 23, this current reaching its full magnitudeat a time t3 at which the current iv drops to substantially zero. If,now the current in biasing winding 15 is so phased as to leave core 9unsaturated or incompletely saturated in the direcu tion of the negativehalfcycle of phase current iv, then the onset of this negativehalf-cycle may be effectively delayed until a time l5, wherebysubstantially no current will tlow through contacts 20, 21 bridged bythe connector 2.5. This establishes a period trs-t of safe cut-out `forthis connector, hence the latter may be arranged to break without arcingat some intermediate instant as indicated at t4. The closed period TK ofconnector 25, being of the same length as the closed period ofconnectors Z4 and 26 under like operating conditions, thus extendsbetween instants to and t4 as shown in graph (c).

If, for some reason, the flow of direct current through load 29 shouldchange, the governor 76 will immediately respond with a correctivedisplacement of the shaft 65 of variometer 66. Let us assume, by way ofexample, that the D.-C. output of the converter has increased and that,as a result thereof, the shaft 65 has been rotated in such a sense(assumed to be counterclockwise) as to delay the phase of the biasingcurrents through windings 14, 15, 16 with respect to that of thevoltages induced in the phase windings 4u, 4v, dw. This reaction willretard the saturation of the core 9 in the direction of current iv,hence this current will reach its full strength only at a time ti'; theeffect of this delay will be the same as if the cut-in had been retardedby an interval t to occur at a time to instead of to. A like apparentdelay, from t2 to t2', will occur at the cut-in of phase 3 and thecurrent iv will only drop to substantially zero at a time ts', theperiod of safe cut-out for the phase v thus being the interval t3t5.Since the time la has been assumed to be subsequent to t4., asubstantial current is would still be passing through the contacts 20,21 at the time of cut-out if the member 25 were to break in the sametime position of the voltage cycle as before. To avoid arcing,therefore, it is desirable to delay the interruption of the connectionbetween these contacts by an interval substantially equal to At, andthis is accomplished as follows:

When the crank arm 64 is swung counterclockwise about its shaft 65, itswings the bell crank lever 58, 61 clockwise about its pivot 62 and,thereby, lowers the rod 71 serving as the common upper lfulcrum for thearms 30, 31, 32. This `adjustment increases the elevation to which thecrescent-shaped cams 48, 49, 50 must raise the pistons 39, 40, 41 inorder to lift the connectors 24, 25, 26 oit their contacts, therebylengthening the closed period of each of these connectors to the desiredvalue of Trr-l-dt. In view, however, of the gently and symmetricallysloping leading and trailing edges of the cams 48, 49, 50, as shown inFig. 2, the time increment At will be distributed between the onset andthe termination of said period, so that without further adjustment thetime of cut-in would be advanced and the time of cut-out would bedelayed by substantially A172 with respect to the old cut-in and cut-outtimes to and It, respectively, as shown in graph (e) of Fig. l. In orderto arrive at the desired delay of the cut-out by At without substantialdisplacement of the moment of cut-in, as shown in graph (4), thedescending roller 57 so acts upon the cam surface of member 55 as torotate the housing 54 of motor 52 in counterclockwise direction, i. e.against the sense of continuous rotation of shaft 53, through a suicientangle to accomplish this result.

It may be mentioned that a replacement of the gently sloping trailingedges of cams 48, 49, 50 by steep, radially directed edges would obviatethe need for a compensatory displacement of the motor housing 54, sincea change in the elevation of fulcrum 71 would no longer aiect the timeof cut-in and would only result in a displacement of the moment ofcut-out in accordance with the slope of the leading edges of these cams;the arrangement actually shown, however, entails the advantage of smoothcontact closure without any chattering.

Referring now to Fig. 4, the operation of the control device 76 will beexplained. In Fig. 4, the conductor 2.3-29 is in series with the loadcircuit as shown in Fig. 2. A D. C. current responsive means 76 is shownwound about this conductor. Such a current responsive means can be aconventional one as described inthe U. S. Patent No. 2,153,378, Fig. lb.The operation of means 76 is to increase or decrease the magnitude ofcurrent ilowing through a circuit including magnetic core 76 andvariable impedance 76". This increase or dccrease in the magnitude ofthe current flow is in response to the-magnitude of the current flow ofthe load circuit.

Beneath the magnetic core 76 is a slide valve 761V. yThis valve isoperated by oil under pressure i'lowing through conduit 11i). Upwardlyextending from the slide valve is a piston 111 downwardly restrained bya compression spring 112. Conduits 113 and 11d extend from slide valve'761V to a servo-transmitter 76V. `Transmitter 76V is in turn coupled tothe shaft 65 of the Variometer 66. It is known that displacement of theservo-mechanism 76V will cause a similar displacement of the variometershaft 65.`

It is apparent that the piston 111 of the slide valve can be movedupwardly against the action of the spring 112 by the magnetic eld set upby the core 76". An increase of the magnetic lield causes the piston tobe moved upwardly so that oil iiows to servo-mechanism 76V in conduit113 and iiows back in conduit 114. This will result in a clockwiserotation of the core of servomechanism 76V and a similar rotation of theshaft 65.

Conversely a downward movement of the piston 111 will cause oil to ilowto the servo-mechanism in conduit 114 and return in conduit 113 with aconcomitant counterclockwise rotation of the servo-mechanism 76V. yIt isapparent that the strength of the magnetic eld set up by the magneticcore 76' depends directly on the magnitude of current owing in the loadcircuit 23-29.

Fig. 3 illustrates a modiiied converter accor-ding to the invention,only so much of the mechanism common to both embodiments having beenillustrated as is necessary for an understanding of the distinctionbetween the systems of Figs. 2 and 3.

In Fig. 3 the means for shifting the phase of the biasing currents forthe reactors 5, 6, 7 take the form of a -circuit arrangement for varyingthe magnitude of a component of each of thesek currents. Thus in Fig. 3

the reactor cores 8, 9, are each shown provided with a rst biasingwinding 92, 93, 94, respectively, connected directly to conductors 70leading to respective bus bars 1, and with a second biasing winding 89,90, 91, respectively, connected via leads 87 to the variable taps 84,85, 86 of respective rheostats 9'7, 96, 95 which are in turn connectedto respective ones of the conductors 70. The contact arms 81, 82, 83 ofthe rheostats 97, 96, 95 are carried on a shaft 80 which takes the placeof a variometer shaft 65 of Fig. 2, being positionable under the controlof governor 76 by means of linkage '77. The system of levers 63, 64,etc. is connected with the shaft Si?.

It will be noted that the biasing current delivered to each of thereactors 5, 6, 7 of Fig. 3 is composed of a xed and a variable vector ofdifferent phases, the xed vector being impressed upon the windings 92,93, 94 via conductors 88, the variable vector being furnished towindings 89, 915, 91 via conductors 87 and rheostats 97, 96, 95 (whichmay be purely ohmic). Since the phase of the biasing current willmarkedly change with Variations of the magnitude of the currentcomponents passed by the rheostats, it will be apparent that the systcmof Fig. 3 will function in precisely the manner described for thepreceding embodiment with reference to Fig. l.

yl't will be understood that the adjustment of a phasing device asrepresented by shaft 65 or 80 need not occur under t'he control of aconstant-current regulator, such as governor '76, bu-t may be effectedmanually or in some other manner for the purpose of producing a variableoutput. Particularly in the latter case, and with highpower converters,it will be desirable to limit adjustments by the herein disclosedcontrol means to a relatively narrow range of output voltages (or outputcurrents), e. g. within about 10%, and to provide conventional voltagedivider means or the like for coarse stepby-step regulation, whereby theloss factor and voltage harmonics will be kept small. It will further beappreciated that additional reactance means, preferably inductances witharmatures of high-quality, low-loss material (e. g. of a laminationthickness less than 0.05 mm.), may be connected in series with theconverter contacts for the purpose of minimizing the currenttherethrough in the event of slight accidental displacement of themoment of cut-in with respect to the precise point of intersection ofthe phase voltages. Such inductances may act as chokes capable ofreducing the cut-in current for periods of the order of from lO-4 to11)-5 seconds to small values, e. g. between 1 and 5 amperes, wherebyarcing will be substantially avoided even where the synchronizationbetween the contact control mechanism and the phasing of the inputvoltages is not perfect; this will enable the construction of adjustablemechanical converters according to the invention designed for relativelyhigh voltages per rectifier unit.

The invention is, of course, not limited to the specic embodimentshereinabove described and illustrated; thus it may be mentioned that thebiasing windings of the reactors S, 6, 7 need not be energized directlyfrom the mains it but that they may be connected to any other convenientsource of current whose output is harmonically related to the mainsfrequency. It will also be apparent that the principles herein disclosedmay be utilized, with obvious modifications, in converters whosealternatingcurrent input comprises more or less than three phases.Furthermore, the motor shaft 51 or its equivalent may be arranged toopen and to close each associated pair of contacts, such as i3, 19, morethan once during each revolution. These and other modifications andadaptations will be readily apparent to persons skilled in the art andare deemed to be embraced within the spirit and scope of the inventionas defined in the appended claims.

What is claimed as new and desired to be secured by Letters Patent is:

1.V In a contact converter, in combination, a load cir'- cuit includinga pair of contacts, a source of alternating voltage in series with saidcontacts, mechanism for periodically opening and closing said contactsin step with said voltage, said mechanism being synchronized with saidsource for invariably closing said contacts at a time when the voltageacross said contacts is substantially zero, saturable electromagneticreactance means connected in said circuit as a variable impedance inseries 4with said contacts, biasing means for said reactance meansperiodically varying the degree of saturation thereof, thereby changingthe value of said impedance, and adjusting means for so synchronizingsaid biasing means with said mechanism as to delay the rise of currentin said circuit, following the closure of said contacts, for a selectedlength of time.

2. ln a contact converter, in combination, a load circuit including apair of contacts, a source of alternating voltage in series with saidcontacts, mechanism for periodically opening and closing said contactsin step with said voltage, saturable electromagnetic reactance meansconnected in said circuit as a variable impedance in series with saidcontacts, biasing means for said reactance means periodically varyingthe degree of saturation thereof, thereby changing the value of saidimpedance, said biasing means including a source of current of afrequency harmonically related to the frequency of said voltage source,said mechanism being synchronized with said voltage source forinvariably closing said contacts at a time when the voltage across saidcontacts is substantially zero, and adjusting means for so phasing saidcurrent source with respect to said voltage source as to maintain saidimpedance at a value sutiiciently large, and for a suicient length oftime following closure of said contacts, so as to delay the rise ofcurrent in said circuit for a selected period following said closure.

3. In a contact converter, in combination, a load circuit including apair of contacts, a source of alternating voltage in series with saidcontacts, mechanism for periodically opening and closing said contactsin step with said voltage, saturable electromagnetic reactance meansconnected in said circuit as a variable impedance in series with saidcontacts, biasing means for said reactance means periodically varyingthe degree of saturation thereof thereby changing the value of saidimpedance, said biasing means including a source of current of afrequency harmonically related to the frequency of said voltage source,said biasing means causing said impedance to assume relatively highvalues at least twice during each cycle of said alternating Voltage,adjusting means for so phasing said current source with respect to saidvoltage source as to maintain said impedance at said relativelyhigh-value for a selected length of time following the appearance of avoltage node across said contacts, and control means so synchronizingsaid mechanism with said biasing means as to cause said contacts toclose invariably at the instant of said voltage node and to open at asubsequent instant when said impedance is again so high as to reduce theflow of current through said contacts to substantially zero.

4. In a contact converter, in combination, a load circuit including apair of contacts, a source of alternating voltage in series with saidcontacts, mechanism for periodically opening and closing said contacts,said mechanism having an operating cycle equal to a cycle of saidalternating voltage, first regulator means for Varying the length of theclosed-contact portion of said operating cycle, second regulator meansfor varying the phase of said operating cycle relative to saidalternating voltage, saturable electromagnetic reactance means connectedin said circuit as a variable impedance in series with said contacts,biasing means for said reactance means periodically varying the degreeof saturation thereof, thereby changing `the value of said impedance,said bia-sing means including a source cf current of a frequencyharmonically related to the frequency of said voltage source, saidbiasing means causing said impedance to assume relatively high values atleast twice during each cycle of said alternating voltage, adjustingmeans for so phasing said current source with respect to said voltagesource as to maintain said impedance at said relatively high value for aselected length of time following the appearance of a voltage nodeacross said contacts, and control means so operating said first andsecond regulator means as to cause said closed-contact portion to startinvariably at the instant of said voltage node and to end at asubsequent instant, varying with different phasing of said currentsource with respect to said voltage source, at which said impedance isagain so high as to reduce the flow of current through said contacts tosubstantially zero.

5. In a contact converter, in combination, a load circuit including apair of contacts; a source of alternating voltage in series with saidcontacts; mechanism for periodically Opening and closing `said contacts,said mechanism comprising a rotating shaft, a contact-operating member,cam means on said shaft co-operating with said member, and supportingmeans for said member adjustable to vary `the length of time duringwhich said cam means is effective to open and to close said contactsduring each operating cycle of said mechanism, said operating cyclebeing equal to a cycle of said alternating voltage; saturableelectromagnetic reactance means connected in said circuit as a variableimpedance in series with said contacts; biasing means for said reactancemeans periodically varying the degree of saturation thereof, therebychanging the value of said impedance, said biasing means including asource of current of a frequency harmonically related to the frequencyof said voltage source, said biasing means causing said impedance toassume relatively high values at least twice during each cycle of saidalternating voltage; adjusting means for so phasing said current sourcewith respect to said voltage source as to maintain said impedance atsaid relatively high value for a selected length of time following theappearance of a voltage node across said contacts; and control means forso synchronizing said mechanism with said biasing means as to cause saidcontacts to close invariably at the instant of said voltage node and tore-open at a subsequent instant, varying with diiferent phasing of saidcurrent source with respect to said voltage source, at which saidimpedance is again so high as to reduce the ow of current through saidcontacts to substantially zero, said control means including means foradjusting said supporting means.

6. ln a Contact converter, in combination, a load circuit inciuding apair of contacts; a source of alternating voltage in series with saidcontacts; mechanism for periodically opening and closing said contacts,said mechanism comprising a motor with a housing and a shaft rotating insaid housing, a contact-operating member, cam-means on said shaftco-operating with said member, supporting means for said member, iirstregulator means for so displacing said supporting means with respect tosaid cam means as to vary the length of time during which said cam meansis effective to open and to close said contacts during each operatingcycle of said mechanism, s id operating cycle being equal to a cycle ofsaid alternating voltage. and second regulator means for varying thephase of said operating cycle relative to said alternating voltage byrotating said housing; saturable electromagnetic reactance meansconnected in said circuit as a variable impedance in series with saidcontact-s; -biasing means tor said reactance means periodically varyingthe degree of saturation thereof, thereby changing the value ot saidimpedance, said biasing means including a source of current of afrequency harmonically related to the frequency of said voltage source,said `biasing means causing said impedance to assume relatively highvalues at least twice during each cycle of said alternating voltage;

adjusting means for so phasing said current source with respect to saidvoltage source as to maintain said impedance at said relatively highvalue for a selected length of time following the appearance of avoltage node across said contacts; and means including said iirst andsecond regulator means for so synchronizing said mechanism with saidbiasing means as to cause said contacts to close invariably at theinstant of said voltage node and to reopen at a subsequent instant,varying with different phasing of said current source with respect tosaid voltage source, at which said impedance is again so high as toreduce the How ot current through said contacts to substantially zero.

7. in a contact converter, in combination, a load circuit: including apair of: contacts, a source of alternating voltage in series with saidcontacts, mechanism for periodically opening and closing said contactsin step with said voltage, a saturable-core reactor including a mainwinding connected in said circuit as a variable impedance in series withsaid contacts, said reactor being provided with at least one biasingwinding, an energizing circuit for said `biasing winding connecting thelatter to said source and including phase-shifting means, saidphase-shitting means Ibeing operable to maintain said impedance at arelatively high value for a selected length of time following theappearance of a voltage node across said contacts, and control means sosynchronizing said mechanism with said phase-shifting means as to causesaid contacts `to close invariably at the instant of said voltage nodeand to re-open at a subsequent instant, determined by the position otsaid phase-shifting means, at which said impedance is again so high asto reduce the iiow of current through said contacts to substantiallyzero.

8. in a contact converter, in combination, a load circuit including apair of contacts, a source of alternating voltage in series with saidcontacts, mechanism for periodically opening and closing said contactsin step with said voltage, 4a saturablc-core reactor including a mainwinding connected in said circuit as a variable impedance in series withsaid contacts, said reactor being provided with a lirst and a secondbiasing winding, a first energizing circuit connecting said lirstbiasing winding to said source, a second energizing circuit connectingsaid second biasing winding to said source, said two energizing circuitscarrying currents of different phase, amplitude-varying means in saidsecond energizing circuit adapted effectively to vary the phase of thealternating electromagnetic field due to the combined effect of saidcurrents, said amplitudevarying means being thus operable to maintainsaid impedance at a relatively high value for `a selected length ot timefollowing the appearance of a voltage node across said contacts, andcontrol means so synchronizing said mechanism with saidamplitude-varying means `as to cause said contacts to close invariablyat the instant of said voltage node and to re-open at a subsequentinstant, determined by the position ot said amplitude-varying means, atwhich said impedance is again so high as to reduce the iiow of currentthrough said contacts to substantially zero.

9. ln a contact converter, in combination, a load circuit including apair of contacts, a source of alternating voltage in series with saidcontacts, an operating member for periodically opening and closing saidcontacts, a motor having a housing and a shaft rotating in said housing,cam means on said shaft controlling said operating member anddetermining an operating cycle therefor equal vto a cycle of saidalternating voltage, supporting means for said member displaceablc withrespect to said cam means so as to vary the length of time during whichsaid cam means is eective to open and to close said contacts during saidoperating cycle, a saturable-core reactor including a main windingconnected in said circuit as a variable impedance in series with saidcontacts, said reactor being provided with at least one biasing-winding,an energizing circuit for said :biasing winding connecting the lat-terto said source and including phase-shifting means, said phase-shiftingmeans being operable to maintain said impedance iat a relatively highvalue for a selected length of time following the appearance of avoltage node across said contacts, rst regulator means connecting saidphaseshifting means to said supporting means for displacing the latterin dependence upon the position or" said phaseshifting means, and secondregulator means connecting said housing to said phase-shifting means forrotating said housing simultaneously with the displacement of saidsupporting means, said first and second regulator means by theircombined action causing said contacts to close invariably at the instantof said voltage node and to re-open at a subsequent instant, determinedby the position of said phaseshifting means, at which sai-d impedance isagain so high as to reduce the .flow ot' current through said contactsto substantially zero.

i0. A contact converter comprising a plurality of input circuits eachenergized by a respective phase voltage of a polyphasealternating-current source, a respective pair of contacts in each ofsaid input circuits, a load circuit connected across all of said inputcircuits, mech anisms for periodically opening7 and closing 'all of saidpairs of contacts with staggered closure periods, said mechanism beingsynchronized with said source for invariably closing each pair ofcontacts at a time when the voltage -thereacross is substantially zero,variable impedance means in each of said input circuits, control meansperiodically increasing and decreasing the impedance of each of saidvariable impedance means so as to delay the rise of current in each ofsaid input circuits for a variable period following `the closure of therespective pair of conta-cts, and adjusting means coupled with saidcontrol means for varying the length of said period by modifying therhythm of operation of said control means.

l1. A contact converter comprising a plurality of input circuits eachenergized by a respective phase voltage of a polyphasealternatingecurrent source, a respective pair of contacts in each ofsaid input circuits, a load circuit connected across all of said inputcircuits, mechanism for periodically opening and closing all of saidpairs of contacts with overlapping closure periods, said mechanism beingsynchronized with said source for in- Variably closing each pair ofcontacts at Va time when the voltage thereacross is substantially zero,saturable electromagnetic reactance means connected in each of saidinput circuits as a variable impedance in series with the respectivepair of contacts, biasing means for each of said 4reactance meansperiodically varying the degree of saturation thereof, thereby changingthe value of said impedance, and adjusting means lfor so synchronizingsaid biasing means with said mechanism as to delay the rise `of currentin each of said input circuits, following the closure of the respectivepair of contacts, for a selected length of time.

l2. A yContact converter comprising a plurality of input circuits eachenergized by a respective phase voltage of a polyphasealternating-current source, a respective pair of contacts in each ofsaid input circuits, a load circuit connected across all of said inputcircuits, mechanism for periodically -opening and closing all of saidpairs of contacts with overlapping closure periods, reactive means insaid load circuit tending to maintain constant the total ilow of currenttherein, thereby causing the phase current in any of said input circuitsto decay following the closure of said contacts in another of said inputcircuits and the rise of the phase current within the latter, saturableelece tromagnetic reactance means connected in each of said inputcircuits as a variable impedance in series with the respective pair ofcontacts, biasing means for each of said saturable reactance meansperiodically varying the degree of saturation thereof, thereby changingthe value of said impedance, said mechanism being synchronized with saidsource for invariably closing the pair of contacts of a given inputcircuit -at the instant when ythe phase voltage of said input circuitintersects the phase voltage of the input circuit previously closed andfor opening the contacts of said previously closed circuit at a timewhen the phase current in the latter circuit has substantially decayed,and adjusting means for so synchronizing said biasing means with saidsource as to maintain said impedance of each input circuit 'at arelatively high value for a selected period following closure of itsrespective pair of contacts.

13. A contact converted comprising a plurality of input circuits eachenergized by a respective phase voltage of a polyphasealternating-current source, `a respective pair `of contacts in each ofsaid input circuits, a load circuit connected across all of said inputcircuits, mechanism for periodically opening yand closing all of saidpairs of contacts with overlapping closure periods, reactive means insaid load circuit tending to maintain constant the total iiow of currenttherein, thereby causing the phase current in any of lsaid inputcircuits to `decay following the closure of said contacts in another olsaid input circuits and the `rise of the phase current within thelatter, saturable electromagnetic reactance means connected in each ofsaid input circuits as a variable impedance in series with therespective pair of contacts, biasing means for each of said saturablereactance means periodically varying `the degree of saturation thereof,thereby changing the value of said impedance, said mechanism beingsynchronized with said source for invariably closing the pair ofcontacts of a given input circuit at the instant when lthe phase voltageof said input circuit intersects the phase voltage of the input circuitpreviously closed and for opening the contacts of said previously closedcircuit at la time when the phase current in the latter lhassubstantially decayed, and adjusting means for so synchronizing saidbiasing means with said source as to maintain said impedance of eachinput circuit lat a relatively high value for a selected periodfollowing closure of its respective pair of contacts and again at aboutthe time of re-opening of said contacts, thereby helping to maintain theflow of current through said contacts at negligible values lat the timeof their re-opening.

14. A contact converter comprising a plurality of input circuits eachenergized by a respective phase voltage of a polyphasealternating-current source, a respective pair of contacts in each ofsaid input circuits, mechanism for periodically opening and closing allof said pairs of contacts with overlapping closure periods, saidmechanism having an operating cycle equal to a cycle of said polyphasesource, first regulator means for simultaneously varying the length ofthe closure periods for all of said pairs of contacts, second regulatormeans for varying the phase of said operating cycle relative to theoutput of said source, a load circuit connected across all of said inputcircuits, reactive means in said load circuit tending to maintainconstant the total ilow of current therein, thereby causing the phasecurrent in any of said input circuits to decay following the closure otsaid contacts in another of said input circuits and the rise of thephase current within the latter, saturable electromagnetic reactancemeans connected in each of said input circuits as a variable impedancein series with the respective pair of contacts, biasing means for eachof said saturable reactance means periodically varying the degree ofsaturation thereof, thereby changing the value of said impedance,control means so operating said first and second regulator means asinvariably to close the pair of contacts of a given input circuit at theinstant when the phase voltage of said input circuit intersects thephase voltage of the input circuit previously closed, said biasing meanscausing the impedance of each input circuit to reach a irst peak atabout the time of closure of its contacts and to reach a second peakroughly half a cycle thereafter, and adjusting means coupled with saidbiasing means and with said control means for displacing said peaks withrespect to said time of closure, thereby delaying the rise of current ineach input circuit for a selectively variable period, and for timing there-opening of each pair of contacts to occur substantially at a timewhen the impedance of the respective input circuit is at its said secondpeak.

l5. A contact converter comprising a plurality of input circuits eachenergized by a respective phase voltage of a polyphasealternating-current source; a respective pair of contacts in each ofsaid input circuits; mechanism for periodically opening and closing allof said pairs ot' contacts with overlapping closure periods, saidmechanism comprising a rotating shaft, a respective operating member foreach of said pairs of contacts, respective cam means on said shaft foreach of said operating members, and supporting means for all of saidoperating members adjustable to vary the length of time during whicheach of said cam means is effective to open and to close the associatedpair of contacts during each operating cycle of said mechanism, saidoperating cycle being equal to a cycle of said polyphase source; a loadcircuit connected across all of said input circuits and includingreactive means tending to maintain constant the total flow of current insaid load circuit, thereby causing the phase current in any of saidinput circuits to decay following the closure of said contacts inanother of said input circuits and the rise of the phase current withinthe latter; saturable electromagnetic reactance means connected in eachof said input circuits as a variable impedance in series with respectivepair of contacts; biasing means for each of said saturable reactancemeans periodically varying the degree of saturation thereof, therebychanging the value of said impedance; control means so operating saidmechanism as invariably to close the pair of contacts of a given inputcircuit at the instant when the phase voltage of said input circuitintersects the phase voltage of the input circuit previously closed,said control means including means for adjusting said supporting means,said biasing means causing the impedance of each input circuit to reacha first peak at about the time of' closure of its contacts and to reacha second peak roughly half a cycle thereafter; and adjusting meanscoupled with said biasing means and with said control means fordisplacing said peaks with respect to said time of closure, therebydelaying the rise of current in each input circuit for a selectivelyvariable period, and for timing the re-opening of each pair of contactsto occur substantially at atime when the impedance of the respectiveinput circuit is at its said second peak.

16. A contact converter comprising a plurality of input circuits eachenergized by a respective phase voltage of a polyphasealternating-current source; a respective pair of contacts in each ofsaid input circuits; mechanism for periodically opening and closing allof said pairs of contacts with overlapping closure periods, saidmechanism comprising a motor with a housing and a shaft rotating in saidhousing, a respective operating member for each of said pairs ofcontacts, respective cam means on said shaft for each of said operatingmembers, supporting means for all of said operating members, rstregulator means for so displacing said supporting means with respect toall of said cam means as to vary the length of time during which each ofsaid cam means is effective to open and to close the associated pair ofcontacts during each operating cycle of said mechanism, said operatingcycle being equal to a cycle of said polyphase source, and secondregulator means for varying the phase of said operating cycle relativeto the output of said source by rotating said housing; a load circuitconnected across all of said input circuits and including reactive meanstending to maintain constant the total flow of current in said loadcircuit, thereby causing the phase current in any of said input circuitsto decay following the closure of said contacts in another `of saidinput circuits and the rise of the phase current Within the latter;saturable electromagnetic reactance means connected in each of saidinput circuits as ia variable impedance in series with the res ectivepair of contacts; biasing means for each of said saturable reactancemeans periodically varying the degree of saturation thereof, therebychanging the value of said impedance; control means so operating saidlirst and second regulator means as invariably to close the pair otcontacts of a given input circuit at the instant when thc phase voltageof said input circuit intersects the phase voltage of the input circuitpreviously closed, said biasing means causing the impedance of eachinput circuit to reach a rst peak at about the time of closure of itscontacts and to reach a second peak roughly half a cyclc thereafter; andadjusting means coupled with said biasing means and with said controlmeans for displacing said peaks with respect to said time of closure,thereby delaying the risc of current in each input circuit for aselectively variable period, and for timing the re-opening of each pairof contacts to occur substantially at a time when the impedance of therespective input circuit is at its said second peak.

17. A contact converter comprising a plurality of input circuits eachenergized by a respective phase voltage of a polyphasealternating-current source, a respective pair of contacts in each ofsaid input circuits, mechanism for periodically opening and closing allof said pairs of contacts with overlapping closure periods, saidmechanism having an operating cycle equal to a cycle of said source, aload circuit connected across all of said input circuits and includingreactive means tending to maintain constant the total flow of current insaid load circuit, thereby causing the phase current in any of saidinput circuits to decay following the closure of said contacts inanother of said input circuits and the rise of the phase current Withinthe latter, a plurality of saturable-core reactors each including a mainWinding connected in a respective one of said input circuits as avariable impedance in series with the respective pair of contactsthereof, each of said reactors being further provided with at least onebiasing Winding, an energizing circuit for said biasing windingsconnecting the latter to said source and including phaseshifting means,control means so operating said mechanism as invariably to close thepair of contacts of a given input circuit at the instant when the phasevoltage of said input circuit intersects the phase voltage of the inputcircuit previously closed, said energizing circuit causing the impedanceof each input circuit to reach a first peak at about the time of closureof its contacts and to reach a second peak roughly half a cyclethereafter, and adjusting means coupled with said phase-shifting meansand with said control means for displacing said peaks with respect tosaid time of closure, thereby delaying the rise of current in each inputcircuit for a selectively variable period, and for timing the reopeningof each pair of contacts to occur substantially at a time when theimpedance of the respective input circuit is at its said second peak.

18. A contact converter comprising a plurality of input circuits eachenergized by a respective phase voltage of a polyphasealternating-current source, a respective pair of contacts in each ofsaid input circuits, mechanism for periodically opening and closing allof said pairs of contacts with overlapping closure periods, saidmechanism having an operating cycle equal to a cycle of said source, aload circuit connected across all ot said input c:4 nits and includingreactive means tending to mainta constant the total flow of current insaid load circuit, thereby causing the phase current in any of saidinput circuits to decay following the closure of said contacts inanother of said input circuits and the rise of the phase current withinthe latter, a plurality of saturable-core reactors each including a mainWinding connected in a respective one of said input circuits as avariable impedance in series withl the respective pair of contactsthereof, each of said reactors being further provided with a rst and asecond biasing winding, a first energizing circuit connecting said firstbiasing windings to said source, a second energizing circuit connectingsaid second biasing windings to said source, said two energizingcircuits delivering currents of diferent phase to the biasing windingsof each of said reactors, amplitudevarying means in said secondenergizing circuit adapted efectively to vary the phase of thealternating electromagnetic eld of each reactor due to the combinedeifect of the currents in its biasing windings, control means sooperating said mechanism as invariably to close the pair of contacts ofa given input circuit at the instant when the phase voltage of saidinput circuit intersects the phase voltage of the input circuitpreviously closed, said energizing circuits causing the impedance ofeach input circuit to reach a rst peak at about the time of closure ofits contacts and to reach a second peak roughly half a cycle thereafter,and adjusting means coupled with said amplitude-varying means and withsaid control means for displacing said peaks with respect to said timeof closure, thereby delaying the rise of current in each input circuitfor a selectively variable period, and for timing the reopening of eachpair of contacts to occur substantially at a time when the impedance ofthe respective input circuit is at its said second peak.

19. A contact converter comprising a plurality of input circuits eachenergized by a respective phase voltage of a polyphasealternating-current source, a respective pair of contacts in each ofsaid input circuits, a plurality of operating members each adaptedperiodically to open and to close a respective one of said pairs ofcontacts, a motor having a housing and a shaft rotating in said housing,respective cam means on said shaft for each of said operating members,said cam means being positioned on said shaft in staggered relation foreffecting closure of said pairs of contacts during overlapping periods,supporting means for said operating members displaceable with respect tosaid cam means so as to vary the length of time during which each ofsaid cam means is elective to close the associated contacts in thecourse of an operating cycle equal to a cycle of said source, a loadcircuit connected across all of said input circuits and includingreactive means tending to maintain constant the total ow of current insaid load circuit, thereby causing the phase current in any of saidinput circuits to decay following the closure of said contacts inanother of said input circuits and the rise of the phase current withinthe latter, a plurality of saturable-core reactors each including a mainwinding connected in a respective one of said input circuits as avariable impedance in series with the respective pair of contactsthereof, each of said reactors being further provided with at least onebiasing winding, an energizing circuit for said biasing windingsconnecting the latter to said source and including phase-shifting means,first regulator means connecting said phase-shifting means to saidsupporting means for displacing the latter in dependence upon theposition of said phase-shifting means, second regulator means connectingsaid housing to said phase-shifting means for rotating said housingsimultaneously with the displacement of said supporting means, saidfirst and second regulator means by their combined action causing thepair of contacts of any of said input circuits to close invariably at atime when the phase voltage of such input circuit intersects the phasevoltage of the input circuits previously closed, said energizing circuitcausing the impedance of each input circuit to reach a rst peak at aboutthe time of closure of its contacts and to reach a second peak roughlyhalf a cycle thereafter, and adjusting means coupled with saidphase-shifting means and with said first and second regulator means fordisplacing said peaks with respect to said time of closure, therebydelaying the rise of current in each input circuit for a selectivelyvariable period, and for timing the re-opening of each pair of contactsto occur substantially at a time when the impedance of the respectiveinput circuit is at its said second peak.

References Cited in the tile of this patent UNITED STATES PATENTS2,181,152 Rolf Nov. 28, 1939 2,227,937 Koppelmann Ian. 7, 1941 2,557,739Goldstein et al. June 19, 1951 FOREIGN PATENTS 881,582 France Apr. 29,1943

